Which party cannot participate in the Reexamination process?

In the context of the reexamination process, a third party cannot participate directly in the process once it has been initiated. Reexamination is specifically designed to allow the original patent owner, the applicant, to address issues concerning the patent's validity based on prior art. This is an important aspect of the system that protects the interests of the patent owner, allowing them to defend their invention against claims, and does not encourage direct involvement from outside parties once the proceedings have started.

The applicant has a vested interest in the process, as they are defending their granted patent, and the patent examiner and the USPTO play crucial roles in evaluating the merits of the reexamination request and maintaining the patent office's integrity. Thus, while the USPTO and patent examiner are integral to the process, third parties are restricted from participating in the reexamination itself.